Learning from nature: Flexible cross-linkable full-bio-based waterborne S-PEEK sizing agent for constructing “hard-soft” structure on CF surface towards superior performance of CF/PEEK composites

Abstract

The recently reported waterborne cross-linkable PEEK sizing agents have garnered considerable attention for refining the interfacial interaction and solvent-resistance of CF/PEEK composites. Nevertheless, the resultant stiff crosslinked structure has rendered the interphase brittle, seriously affecting the stress transfer and energy dissipation of composites. Inspired by the “hard-soft” components found in the robust pearl shells of nature, sebacic acid derived fluoride (F-AC) and magnolol have been employed to elaborate a flexible, cross-linkable, full-bio-based waterborne S-PEEK sizing agent, aimed at bolstering the mechanical strength of CF/PEEK. Additionally, the T_g and T_5% of S-PEEK were 61 °C and 442 °C, respectively. The particle size range of the waterborne S-PEEK sizing agents spanned from 184 to 286 nm. Notably, the cross-linked structure generated by the allyl groups within magnolol during the processing stage of CF/PEEK serves as the hard components, whereas the long-chain fatty segments of F-AC acts as the soft constituents. This combination constructs a biomimetic hard-soft structure on the CF surface, maximizing the advantages of rigid structures by incorporating soft components. Additionally, it collaboratively contributes to energy dissipation, prevents stress concentration, and mitigates the risk of brittle fracture in composites. Specifically, the bending strength, interfacial and interlaminar shear strength of CF/PEEK experienced respective increases of 40.71, 77.53 and 62.62 % compared to pristine CF/PEEK following sizing treatment. Notably, even after enduring 72 h of solvent aging, the mechanical integrity was preserved at approximate 95 %. Our work is expected to provide a promising strategy for fulfilling the distinguished capabilities of CF/PEEK in the future.